Wood fiber for high-grade paper and derivative manufacture



Patented Apr. 16, 1929.

UNITED STATES PATENT OFFICE.

GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY, OF BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE.

WOOD FIBER FOR HIGH-GR/ADE PAPER AND DERIVATIVE MANUFACTURE.

No Drawing.

This invention has for its object to produce a new product, namely a chemical wood pulp,

, which by reason of its characteristics is capable of uses to which commercial wood pulp 6 is not fitted or adapted.

More particularly the object of the present invention is to produce a pulp consistin of cellulose derived from wood characterizet by a high alpha-cellulose content comparable 10 with pulp derived from cotton fibers, by its capacity to be hydrated when subjected to the usual beating operation, by a minimum content of impurities, such as lignins, resins and pentosans, by softness of texture and high absorbency. A product having these characteristics maybe employed in the manufacture of high grade paper where softness of texture, tearing strength and superior folding or flexing qualities are important, and in the manufacture of celtulose esters or products such as viscose, cellulose nitrate and vulcanized fiber (such for example as produced by the use of zinc chloride).

I shall herein describe a process by which unbleached pulp, such as derived from spruce wood by the cooking thereof in an acid sulphite (either sodium or calcium base) or sodium sulphate-sulphite solution, may be so treated as to produce a maximum yield of the fore mentioned, at a relatively low cost,

whereby the process may be carried on commercially and continuously;'but I do not herein claim such process per se, as it forms the subject-matter of the copending application Serial No. 716,154,filed May 27, 1924-.

At the present-time it is the commercial practice, in the manufacture of high grade paper having the properties to which I have referred, to employ as the raw material new cotton rags, and, in the manufacture of c'elluproduct having the characteristics hereinbe- Application filed November 7, 1924. Serial No. 748,502.

cellulose. The beta. and the gamma cellulose represent components which are unstable when exposedto light, moisture, oxygen and alkahes; whereas the alpha cellulose is highly resistant to these agencies. Cotton is charviously produced commercially, has an alpha cellulose content ranging from 83% to 86%, and a correspondingly higher beta and gamma cellulose content than are present in cotton. A pulp produced from cotton fiber is further characterized by a low pentosan content, a very low lignin content, and a low resin and wax content. The pentosan content of a raw or bleached cotton fiber ranges from 0.4% to 1%, its lignin content is usually less than 0.3%, and the resinous and waxlike constituents amount to about 0.3%, of the total weight. On the other hand, the pentosan content of high grade sulphite pulp varies from 3.5% to 5.5%, the lignin content from 0.5% to 3%, andcthe resinous content from 0.5% to more than 1%. Furthermore the paper produced from such sulphite pulp is relatively harsh and nonabsorbent, and has what is referred to as a rattle when a'sheet of the paper is shaken. And, moreover, the paper is much less resistantto tearing action and has a less folding endurance than paper made from cotton fiber. -A gain, because (if-its high beta and gununacellulose content, its high lignin. pentosan and resin content,t-he pulp and the paper produced therefrom is less stable when subjected to alkali, moisture, light and oxygen, and the pulp itself is not as suitable as cotton for use in the production of such cellulose esters and roducts as viscose, cellulose nitrate and the li (e.

The pulp product, which isthe subject of the present invention, has the desirable characteristics of cotton, but it differs from cotton in that it has'a shorter fiber and consequently requires less manipulation in its conversion" into paper, a'nd has the additional very decided advantage over cotton in thatits cost to the consurrrer. is only a fraction of the cost of cotton. It is further distinguishable from cotton when subjected to certain tests which I shall hereinafter describe.

I here present a comparative-table of th three materials, namely cotton, commercial bleached sulphite pulp, and my new product derived from sulphite pulp, to wit-- I Cotton ggg New product Alpha cellulose, 94-98 83-86 93. 5-96 Beta cellulose, 2-3 7-9 2-4 2-3 1 7-5 2-2. 5 6. 3- l 0. 5-3. 0. 3- 99+ 1 97-99 93+ Copper number 0. 6-2 0 3. -5. 5 1. 0-2. 3 Resins, etc, 0. 3i: 0. 5-1. 0 0. 2-0. 4 Pentosans, 5-1. 0 3. 5-5. 5 1. 0-2 4 Fiber length (av.) m. m. 0. 5-. 8m. in. 1. 0-1. 5 m. m. Herzberg fiber stain..-" Wine red. Blue. Reddlsh purple. Soda solubility, (3%

boiling NaOH so lution) 1-20 -30 Not over 9.

N0tc.'1he fibers of cotton are very long. ,Thesc long fibers are not suitable for paper making as such and must be reduced in length, Bi atvn cottpn fiber has approximately the same fiber length as beaten stock made from the new fiber herein described.

It shouldbe noted that some of the identifying characteristics assignedto cotton fiber may vary outside the limits set forth. For

are concerned, but it is distinguishable therefrom and ossesses the advantage of a low cost and a s orter fiber length before beating.

In producing a product having the characteristics herein described, I start with unbleached sulphitepulp silch as produced'by cooking the chips of spruce. inan acid calcium bisulphite or equivalent'acid solution (e. g.,

sodium bisulphite) under conditions of heat and ressure for a sufficient time to produce a pu p .which is comparable with high'grade unbleached pulp such as manufactured at the present time. The starting material is thus derived from wood, and consists of cellulose which has been freed from the encrusted or oemcntitious materials and c pntains specks,

knots, resins, lignin, pcntosamand a relative.- 1y high proportion of beta and gamma celluloses. This starting material is now treated as follows It is preferably first treated as about a 10% stock suspension in a solution containing about 1% to 2% hypochlorite, or-

about0.3% to 0.6% chlorine, based'on the dry weight of fiber, as describedin the hereinbcforeddeptified application for patent.

Whether or not the raw o r unbleached pulp employed as the starting material should be threatd with hypochlorite solution .or chlorine water before alkaline digestion depends upon the characteristics of such pulp. The

'hcrcinbcfore given in the table.

and thereafter rises.

pretreatment may, for example, be omitted when a Well-cooked raw pulp is prepared as the starting material by digesting chipped wood, spruce, for example, in a sodium base acid bisulphite liquor having a combined S9 content of about 1% and a free SQ content of about 5%. But if the usual or commercial unbleached sulphite pulp prepared in calcium bisulphite cookingdiquors is employed as the raw material. it should be treated as hereinbeforcdescribed, with hypochloritesolution or chlorine water before alkaline digestion, as this makes possible the production of a new product having the desirable characteristics As stated in the application hcreinbefore referred to, the

composition or strength of.the hypochloritc.

solution or chlorine water used in thctreatment of the raw pulp before alkaline digestion may be varied, depending upon the particular characteristics of the raw pulp being processed, in order to obtain my new product. As further stated in that application, the first consumption of the oxidizingagent, i. e., the hypochlorite solution or chlorine water, is accompanied by arise in the proportion of alpha cellulose in the pulp, but a critical point is reached at which further consumption of the oxidizing agent is accompanied by a marked decrease in the proportion of the alpha or resistant cellulose content of the pulp. It has been noted that the copper number decreases with the first consumption of. thcoxidizin'g agentup to the critical point, Consequently, in carrying on the first step of the process, I employ a relatively small'amount of oxidizing agent, based on the amount of pulp, and terminate the opration-when orbefore this critical point is reached that is, or approximately at the critical point. It is then subjected to the action of dilute alkaline solution at the boiling temperature of the solution for a period of from 3 to 5 hours in anopen vessel, sulficient heat being supplied to the vessel to maintain the temperature of the contents at the boiling point of the alkaline solution. This solution is preferably one of caustic soda of approximately 0.5% strength. During this treatment the contents of the vessel are continuously agitated to ensu're the permeation of the alkaline solution throughout the mass of pulp. 1 As a result of. this treatment,

the greater part of the less stable c'ellulose,

in the alkaline solution. The lignin, resin,

pentosan contentis for the greater part also dissolved in the solution. Preferably, of course, before the unbleached or'raw. pulp is subjected to this treatment, it is screened for the removal of knots and foreign matter resulting from the digestion.

After the treatment wi h the alkaline solu-' tion, the pulp is washed in any suitable washor for theremoval of the alkaline liquor and the substances which have been dissolved therein, and, if desired, treated with antichlor so that the pulp is now neutral.

The pulp is now subjected to the bleaching action of an oxidizing agent such as calcium hypochlorite. This bleaching operation removes from the treated fiber the remaining traces of coloring matter and produces a white fiber. This bleaching action is accomplished without a sacrifice of alpha cellulose content in the finished fibers. Consequently to this end I employ a minimum amount of bleach amounting to from 3% to 5% of bleach powder based on the weight of dry fiber thus treated. Preferably, the bleach liquor contains a certain proportion of free alkali,- say, caustic soda or sodium carbonate, as described in the hereinbefore identified application for patent, as this tends to prevent the formation of oxycelluloses during bleaching, and thus to reduce the copper number of the bleached product. The fiber is again washed to free it of reaction products caused by the bleaching operation, and is recovered by the usual wet machine in sheet form. The pulp thus produced possesses the characteristics which I have hereinbefore described.

I present hereinafter a table showing the papermaking characteristics of certain cellulosic fibers, namely, raw or unbleached sulphite pulp, bleached sulphite pulp, bleached new rag pulp, and my new product:

Raw Bleached Bleached New sulphite sulphite new rag mduct pulp pulp pulp p Time of beating requisite (or normal papermaking. 3 hrs. 2.5-3 hrs. 10-12 hrs. 7-8 hrs. Pop test (Mullen) 01 resulting paper in points per pound asis weight 60 60 Tearing resistance per basis weight 130 130 300 230 Folding endurance in double folds per basis welght 1 1 20 7-10 Initial color below 93 103-104 110 104-5 chlorine gas dissolved in water for a final I improvement in the color of the fiber. This, however, is not necessary where the pulp is to be employed for the production of cellulose esters or other products, but is sometimes dcsirable where the pulp is to be used in the manufacture of a very white fine paper.

I do not herein claim the subject matter of patent application Serial No. 710,154, filed may 27, 1921, which is concerned with, and has claims directed to, a method of producing a product such as herein described and claimed.

lVhat I claim is 1. A new article of manufacture, consisting of cellulose wood pulp of high whiteness having among others the following characteristics, to wit: an alpha cellulose content of 93.5% to 96%, a beta cellulose content of 2% to 4%, a gamma cellulose content of 2% to 3%, a pentosan content not exceeding 2.4%,

a copper number of 1.0 to 2.3, producing a reddish-purple color when subjected to Herzberg fiber stain, and of a solubility in 8% boiling NaOH solution of not over 9%.

2. A new article of manufacture consisting of wood fiber of high whiteness, having among others the following characteristics, to wit: an alpha cellulose content not less than 93.5%; a pentosan content not exceeding 2.4% a copper number not exceeding 2.3, of a solubility in 3% boiling N aOH solution of not over 9%, and producing a reddish purple color whensubjected to Herzberg fiber stain.

3. A new article of manufacture consisting of a wood fiber possessing the whiteness of new cotton and having, among others, the following characteristics, to wit: an alpha cellulose content of from 93.5% to 96%, a

- pentosan content of from 1.0 to 2.4, a copper number of from 1.0 to 2.3 of a solubility in 3% NaOH solution of not over 9%, said wood fiber being characterized by papermaking properties similar to those of a new rag halfstock.

In testimony whereof I have affixed my signature.

GEORGE A. RICHTER. 

